Traditional power stages of power converters are driven by one or more DC or AC voltage sources. Thus, such converters for providing a regulated electric output are typically based on switching circuits with electric switches configured in a voltage driven topology. Such swithcing circuits are used in many applications, e.g. switch mode power supplies, and they are often implemented with electric switches in the form of MOSFETs.
Normally, power stages convert the input voltage to a regulated output voltage. However, in a few cases, the input voltage is converted into a regulated output current. This is used in some audio power amplifiers which can be designed with a current output to drive a loudspeaker.
However, solar cells, i.e. electric sources converting light into electric energy, can be regarded as current sources. This applies also to AC powerlines, i.e. transport of electric energy in long cables, or in general to applications where an electric source is connected to a converter or a load via cables that can be considered to be long due to the combination of a high AC frequency, a high current level, and long connecting cables. Thus, in practice electric sources in the form of current sources are not that rare, even though typical converters are designed based on the assumption that the electric source can be considered to be a voltage source.
Typically, circuits for converting electric energy from a solar cell, i.e. a current source are configured to receive power from a voltage source, and thus a capacitor across the input terminals is required to initially convert the current from the solar cell to a voltage which is then used to drive the converter circuit. The required extra capacitor increases costs, comprises reliability and lifetime, and due to the required capacitance, it occupies a significant space compared to the other components needed to implement the switching circuit. Finally, the extra capacitor reduces the total power conversion efficiency that can be obtained.